Pathogens Flashcards
What is a pathogen?
Microorganism that is capable of causing disease
How is a pathogen usually identified?
by the set of virulence genes that are carried and expressed
What is the virulence?
Measure of the ability to cause damage to the host, it depends on a number of virulence factors
how is virulence determined? (2 features) are these to mutually exclusive?
Invasiveness
Toxigenicity
Are NOT mutually exclusive
Define invasiveness
ability of the microorganism to become established in the host, to overcome the host defenses and to spread in the tissues
Define toxigenicity
the capacity of the microorganism to produce substances known as toxins that damage SPECIFIC tissues of the host
What are the steps in invasion of a pathogen in a host?
- Exposure
- Adherance
- Invasion
- Colonization and growth
Toxicity
Invasiveness
==> tissue damage, disease
What are difference virulence factors used by the pathogens?
- Adhesins
- Capsules
- Enzymes that destroy host tissues
- Invasins
- Type 3 and 4 secretion systems ( T3SS and T4SS )
Describe adhesins
Promote SPECIFIC attachment to host cell surfaces
One adhesin type is usually able to attach to one or a few cell types, determine the site of colonization
Name 2 types of adhesins
Fimbriae/Pili: polymers, mediate LOOSE attachment
Afimbrial adhesins: (no filaments) mediate CLOSE attachment
What is a capsule?
Guhy substance attached to cell wall, protect pathogens against host immune cells (phagocytes), can also help to attach
For what particular pathogens is capsule really important?
Streptococcus pneumoniae
Haemophilus influenzae
True or false
Capsule is only a virulence factor
False, non pahtogenic microorganisms may have a capsule too
How do pathogens normally penetrate the host tissue?
Penetration of epidermis by using breach in the skin (wounds, surgeries, catheter…)
Penetration of the mucosa by destructing the single-cell layer, or invasion of cells
What are specific extracellular matrix (ECM) prots targeted by the pathogens? (3 prots…)
Hylaluronic acid
Collagen
Fibronectin
What enzyme of pathogens targets hyaluronic acid?
Hyaluronidase: degrades hyaluronic acid, a sticky polysaccharide that holds cells together.
What microorganisms use hyaluronidase enzyme?
Staphylococci
Streptococci
Clostridia
What enzyme is used by pathogens to degrade collagen?
Collagenase: degrades collagen present in connective tissues
What enzyme is used to degrade lecithin?
Lecithinase: degraes lecithin (phosphatidylcholine) in cell membrane, causing lysis of red blood cells and destroying tissue cells
What is gas gangrene? What microorganism causes it?
Infection of deep wound.
By Clostridium perfringens
C.perfringen is strictly anaerobe.
Uses LECITHINASE to lyse host cells, COLLAGENASE and HYALURONIDASE to destroy ECM.
Describe hemolysin
Some are ENZYMES ( lecithinase, phospholipase), some are CYTOLYSINS (pore forming).
Produced by a great variety of bacteria, cause lysis of red blood cells and variety of other cells
What does cytolysin do?
it is a pore-forming toxin, inserts inside the membrane of host cells, create channels, so cell is not impermeable anymore. Cell lysis
What does leucocidin do?
Causes lysis of leucocytes (WHite blood cells)
What organisms produce leucocidin?
Staphylococci
Streptococci
and a fer Gram-negatives
What do proteases do?
Degrade prots and/or antibodies. It is produced by several bacteria
What is coagulase? What mcroorganism produces it?
Produced by virulent STAPHYLOCOCCI
Causes insoluble fibrin to be deposited on bacterial cells and cloaks the bacteria from the immune system.
What are invasins?
Surface prots or injected prots that allow microorganisms to enter cells and invade the host
Can trigger phagocytosis of the the bacteria by the cell
What is the point of invasins?
Way to hide from the immune cells ( by hiding in another cell…)
Also used to provide source of nutrient to the invader
What microorganisms use invasins?
Mycobacterium, salmonella, listeria, chlamydia
what is the problem that pahtogens have to face when invading a host cell? how do they face it?
When they invade a cell and want to use it as source of nutrient (ex by using invasins…) they need to hide from host cell defense mecanism.
They need to modify the properties and behavior of the host cell
What do pathogens do to modify properties or behavior of host cells?
- Block phagosome maturation
- Increase size of vacuole
- Acquire nutrients
- Block detection of intracellular infection and response (host defense)
What special secretion is used by pathogens to take control of host cell? What particular organism use it?
They use T3SS and T4SS ( type 3-4 secretion system )
Used by a large number of gram negative pathogens
What is another name for T3SS and T4SS
injectisomes
What does T3SS do?
forms a channel through the bacterial cytoplasmic membrane, the periplams , the outer membrane and the host cell membrane so bacterial prots can be INJECTED into the host cell cytosol
What is the function of T3SS
Invasion of the host cells
Block phagosomes maturation
Take control of host cells
What is the difference between T3SS and T4SS
T4SS is similar, but absence of needle-like structure
What do we call an extracellular enzyme that cause damages?
TOXIN
Bacterial pathogens are associated with 2 types of diseases: …
- Infectious diseases (pneumonia, menningitis…): result from pathogens GROWTH
- Intoxications (food poisening) : result from the presence of a specific toxin
What are the 2 categories of toxins?
Endotoxins : part of the bacterial pathogen (like LPS)
Exotoxins : secreted into the surrounding as the bacterial pathogen grows
What are some characteristics of exotoxins?
- Soluble
- Secreted or released when the organism is lysed
- Usually proteins
- Usually heat-labile (destroyed by heat)
Does exotoxin respond to antibody activity?
Yes, Highly immunogenic (antibody response inactivates exotoxins )
How are exotoxins categorized?
By their target: - Neurotoxins - Enterotoxins (gastrointestinal tract) - Nephrotoxins (kidney) - Hepatotoxins ( liver) - cardiotoxins .......
What are AB toxins ?
Exotoxins
CAlled Ab because composed of 2 subunits:
- A subunit (enzymatic subunit)
- B subunit ( binding/ cell entry)
What does A subunit from AB toxin do?
Modifies a target inside the host ell leading to damage to the host
( ex: ADP -ribosyltrnasferase)
What does B subunit from AB toxin do?
Binds to specific cell receptors providing tissue/cell type specificity
What is an exemple of AB toxin? What organism produces this toxin?
Botulinum toxin produced by Clostridium botulinum.
What is the effect of Botulinum toxin? What kind of toxin is it?
It is a neurotoxin.
- Blocks acetylcholine release in neuromuscular junction
- Causes flaccid paralysis ( block muscle contraction)
BOTOX: reduces wrinkles etc..
What is the difference between AB5 toxin and AB toxin
AB5 has 5 B subunits
What pathogen produces AB5 toxin?
Vibrio cholerae
What does AB5 toxin do?
subunit A from AB5 toxin will make the cell produce a lot of cAMP. This will make the cell stop to make sodium (that would normally go in blood stream). cAMP will also trigger Cl and HCO3- to enter the lumen, create massive influx of water in lumen–> diarrhea
What is a good know endotoxin? When is it released?
Lipid A of LPS from Gram-negative bacteria.
It is released during multiplication or lysis of bacterial cells
What are some characteristics of endotoxins?
- Heat stable
- Weakly immunogenic (no antibody are produced against LPS)
- VEry effective activator of immune system, produce general systemic effect (fever, septic shock (when blood stops moving))
How do we use vaccins? Against what type of toxin?
Used against exotoxins
- Toxin are first inactivated by heat or formaldehyde, so tehy become TOXOIDS
- Toxoids are no longer toxic, but still antigenic (induce antibody response)
Can vaccins be made against endotoxins?
No,
endotoxins cannot be inactivated by heat or formaldehyde and cannot be converted to a toxoid
NO VACCIN AGAINST ENDOTOXINS
